Preheat the oven to 425°F. Coat a baking sheet with cooking spray or line it with parchment paper; set aside.
cooking spray
In a large bowl, combine the flour, cornmeal, granulated sugar, brown sugar, baking powder, baking soda, and salt. Cut in the butter until the mixture resembles coarse crumbs.
1-1/2 cup all-purpose flour, 2/3 cup yellow cornmeal, 2 tbsps. granulated sugar, 2 tbsps. tightly packed light brown sugar, 1-1/2 tsps. baking powder, 1/4 tsp. baking soda, 1/2 tsp. table salt, 1/3 cup cold butter
Make a well in the center and add the buttermilk, egg, and lime zest. Using a fork, beat the egg and buttermilk together, then stir everything just until moistened—be careful not to overmix.
1/2 cup buttermilk, 1 large egg, 1-1/2 tsps. lime zest
Toss the frozen blueberries with cornstarch to coat, then add them to the dough. Stir gently, about 3 to 5 times, just until the berries are incorporated (do not overmix).
1 cup frozen blueberries*, 1 tsp. cornstarch
Using a large spoon, drop the dough into 12 mounds, leaving about 1 inch of space between them. Bake for 12 to 15 minutes, or until the tops are golden. Transfer immediately to a cooling rack.
For the icing, whisk enough lime juice into the confectioners' sugar in a small bowl until it reaches a drizzling consistency. Drizzle over the warm scones, then sprinkle with almonds. Serve warm.
3-4 tsps. fresh lime juice, 1 cup confectioners' sugar, 3 tbsps. chopped almonds, toasted